DNA molecules exchange parts with each other in a variety of circumstances. In meiosis, eukaryotic chromosomes break and join with strict adherance to homology, so that the order of gene loci is preserved. This process, generalized genetic recombination, will be further investigated in yeast (S. cerevisiae) and phage lambda. A fuller understanding of recombination may have implications for developmental anomolies, immune deficiencies and cancer induction. This continuing investigation will emphasize recombination initiated by double-chain breaks. Such breaks initiate both mitotic and meiotic exchange in yeast and recombination by the Red, RecE and RecF pathways operating on lambda. The RecBCD pathway is, likewise, dependent on double chain breaks, although the induced exchange is remote from the break. The molecular mechanisms involved will be elucidated.